A Simulated Preconditioning of Typhoon Genesis Controlled by a Boreal Summer Madden-Julian Oscillation Event in a Global Cloud-system-resolving Model

A preconditioning of a typhoon genesis over the North Western Pacific by an Madden-Julian Oscillation (MJO) event is simulated in a boreal summer numerical experiment conducted using a global cloud-system-resolving model. The simulation highlights the importance of the following processes in the typhoon genesis that were not clearly captured in the conventional general circulation models: as the MJO propagates over that region, the easterly shear (with an enhanced low-level westerly) of the western branch of the MJO's circulation moderates the climatological westerly shear that is otherwise persistent and inhibits cyclogenesis there. Meanwhile, its attendant cyclonic vorticity from the westerly region migrates northward, causing the genesis to occur. The trough in the upper troposphere at 15 degrees-20 degrees N is found to contribute to the genesis. The result demonstrates the performance of a global cloud-system-resolving model at predicting tropical cyclogenesis associated with the MJO in the North Western Pacific during the active typhoon season in boreal summer.